Quantitative Determination of Grain-Boundary Recombination Velocity in CdTe by Cathodoluminescence Measurements and Numerical Simulations

We present a 2-D numerical model simulating cathodoluminescence (CL) measurements on CdTe. The model is used to analyze the impact of material parameters on the measured CL intensity to establish when grain-boundary (GB) recombination velocity S_GB can be determined accurately from CL contrast. In addition to GB recombination, grain size and its ratio to the carrier diffusion length can impact CL measurements. Holding the grain interior and GB recombination rates constant, we find that as the grain size increases and exceeds the diffusion length, the observed CL contrast increases. For small-grain-size material, surface recombination lowers the overall intensity of the CL signal but does not significantly impact CL contrast. For large grains, high-surface recombination velocity can decrease the CL contrast. The model is combined with experimental results to quantify the S_GB in polycrystalline CdTe before and after the CdCl₂ treatment and to predict the impact of GB recombination on device performance.